This invention relates to silicon-containing acetal protected polymers and photoresist compositions thereof especially useful in bilayer resists.
New, improved, advanced resists are required to manufacture new electronic devices with smaller feature sizes. Typically, improvements are required in photoresist resolution, photospeed, depth of focus, and other properties. Resolution improvements can also be obtained via exposure systems utilizing higher numerical apertures. Unfortunately, as the resolution is improved via higher numerical apertures, the depth of focus at best resolution usually decreases due to optical effects. Thus, improvements in depth of focus of resist are also desirable.
The most common type of resists are called xe2x80x9csingle layerxe2x80x9d resists in which the resist has both the function of imaging and plasma etch resistance. A second type of resist is termed a xe2x80x9cbilayer resistxe2x80x9d in which the upper layer is assigned the function of imaging and the underlayer assigned the function of plasma etch resistance. An oxygen etch step transfers the imaged pattern into the underlayer. Bilayer resists typically contain silicon and provide certain advantages in resolution from using thinner imaging films and in many cases the bilayer resist/undercoat combination provide better substrate plasma etch resistance. Examples of bilayer resists can be found for example in U.S. Pat. Nos. 6,359,078, 5,985,524 and 6,028,154 and other patents, each of which is incorporated herein in their entirety.
Advanced resists usually employ a technique called chemical amplification in which an acid generated by photolysis catalyzes a solubility switch from alkali insoluble to alkali soluble by removal of an acid sensitive group protecting an alkali solubilizing moiety. Polymers frequently used in this type of photosensitive composition include acetals derived from reaction of vinyl ethers with a polymer containing hydroxystyrene units. Chemically amplified resists based on acetal protected polyhydroxystyrene, such as found in U.S. Pat. Nos. 5,928,818, 5,834,531, and 5,558,976, which are incorporated herein by reference, are well known. Preferred characteristics and often advantages over other chemically amplified systems include lower temperature in processing conditions, and lower sensitivity to bake temperature variations.
Many new high resolution photoresists have been found to be dimensionally unstable to typical electron beam-based metrology system. This produces an undesirable uncertainty in the line width measurements, which can lower production device yields. Solutions to this problem are eagerly awaited by the industry.
The present invention also provides many additional advantages which shall become apparent as described below.
A photoresist composition comprising at least one novel acetal group containing polymer having a silicon substituent; provided that the silicon substituent is not directly attached to the acetal functionality, thereby providing high resolution, improved DOF, and improved dimensional stability under metrology conditions.
The photoresist composition preferably comprises a novel polymer formed from a silicon containing monomer unit having the general structure: 
wherein R1 is H, lower alkyl, CH2CO2R, cyano, CH2CN, or halogen, wherein R is any alkyl, cycloalkyl, aryl, aralkyl, alkylenecycloalkyl, silyl or siloxy or linear or cyclic polysiloxane groups; R2 is CHR7R8 where R7 and R8 are H, lower alkyl, cycloalkyl or aryl; A is a substituted or unsubstituted alkylene, cycloalkylene, alkylenecycloalkylene, or alkylenearylene; and R3 is SiR4R5R6 where R4, R5, and R6 are independently alkyl, cycloalkyl, aryl, aralkyl, alkylenecycloalkyl, silyl or siloxy, or linear or cyclic polysiloxane groups or a silsesquioxane alkanol compound.
xe2x80x98Axe2x80x99 is preferably selected from the group consisting of: methylene, ethylene, CH2C(CH3)H, propylene, CH(CH3)CH(CH3)CH(CH3), cyclohexylene, ethylenecyclohexylene, phenyleneethylene, and the like. R3 is preferably selected from the group consisting of: trimethyl silyl, triethyl silyl, triphenyl silyl, tricyclohexylsilyl, tristrimethylsiloxysilyl, tristrimethylsilylsilyl, methyl-bistrimethylsilylsilyl, methylbistrimethylsiloxysilyl, dimethyltrimethylsilylsilyl, dimethyltrimethylsiloxysilyl, and cyclic or linear polysiloxane oligomer or polymers or a silsesquioxane alkanol compound.
The silicon containing monomer unit is typically generated by polymerization of a substituted styrene monomer, followed by reaction of the substituent to yield a hydroxystyrene monomer unit and subsequent reaction of the hydroxystyrene units with a vinyl ether of the structure: 
Typically, acetoxy styrene is polymerized and transacetylized to yield hydroxystyrene monomer units for reaction with the vinyl ether.
Alternatively, the monomer unit can be generated by reaction of the above generated hydroxystyrene monomer units with a vinyl ether and an alcohol of structure:
HOxe2x80x94Axe2x80x94R3xe2x80x83xe2x80x83III
Many vinyl ethers can be used, but secondary and tertiary vinyl ethers provide better incorporation of the alcohol. t-Butyl vinyl ether is preferred.
Alternatively, the monomer unit can be generated by polymerization of the monomer wherein the silicon containing acetal moiety has already been generated. Either reaction of hydroxystyrene monomer with a vinyl ether of the structure given below or reaction of a vinyl ether and the alcohol of the structure given below may be used. xe2x80x83HOxe2x80x94Axe2x80x94R3xe2x80x83xe2x80x83III
The acetal containing polymer is preferably formed by reacting a polymer containing hydroxystyrene units with t-butyl vinyl ether and an alcohol in the presence of an acid catalyst.
The HOxe2x80x94Axe2x80x94R3 alcohol is preferably selected from the group consisting of: trimethylsilyl methanol, trimethylsilyl ethanol, tristrimethylsilyl methanol, tristrimethylsilyl ethanol, tristrimethylsiloxymethanol, tristrimethylsiloxyethanol, methylbistrimethylsilyl ethanol, methyl bistrimethylsiloxy ethanol, tris trimethylsiloxy propanol, methylbistrimethylsiloxy propanol, hydroxymethyl terminated polysiloxane polymers, hydroxyethyl terminated polysiloxane polymers and cyclic siloxanes oligomers, such as that of the structure IV herebelow and caged siloxanes, such as the silsesquioxane alkanol compound V herebelow: 
Optionally, the polymer also comprises an additional monomer unit selected from the group consisting of: hydroxystyrene, hydroxystyrene units blocked with other acid sensitive groups, (meth)acrylates, vinyl ethers or acetates, or substituted and unsubstituted maleimides. Preferably the polymer comprises between about 5 to 75 molar % of the silicon containing monomer and between about 25 to 95 molar % of the additional monomer. More preferably the silicon containing monomer unit is present in an amount between about 5 to 30 molar wt. % and the additional monomer unit is present in an amount between about 70 to 95 molar wt. %.
The acetal containing polymer typically has a molecular weight in the range between about 2,000 to 75,000.
The present invention also include a bilayer resist comprising: a photoresist layer comprising at least one acetal containing polymer having a silicon substituent; provided that the silicon substituent is not directly attached to the acetal functionality; and an undercoat layer.
The present invention also includes a photoresist composition comprising the novel acetal containing polymer having a silicon substituent; provided that the silicon substituent is not directly attached to the acetal functionality; and a photoacid generator compound.